近年來，溫室效應和全球暖化的影響越來越嚴重，造成降雨率持續攀升打破各地紀錄。直升機或旋翼機也是飛機的一種，是利用兩片或是多片的水平主旋翼葉片旋轉推動以產生升力，有懸停和垂直起降特性，利於台灣極端溫差天氣的救災狀況，因而在空中勤務總隊裡廣泛使用，所以大雨中直升機的性能探討分析和發展值得我們深入研究。隨著研究大雨的物理現象，我們利用CFD方法成功估算出標準主旋翼葉片受到大雨時所造成的不利影響現象，因此建議直升機飛行員應該藉此訊息事先加以防範，或增加訓練科目，相信本研究結論能為直升機在惡劣天氣下救援能有所幫助。

In recent years, the greenhouse and global warming effects are becoming more and more severe, that partially explains why rainfall rates keep breaking record in all parts of the world. In general, helicopter or rotorcraft is an aircraft that is lifted and propelled by one or more horizontal main rotors, and it can take off and land vertically. Currently, helicopter has widespread utilization by air rescue unit in Taiwan during disaster situation under extreme weather situations. For this reason the understanding and improvement of helicopters under heavy rain condition is the main theme of this research. With our understanding of heavy rain physics, a CFD tool has first been developed and successfully tested on the standard helicopter blade. Once the heavy rain droplets are added, it is observed that rainfall indeed will decrease the total lift and might induce some detrimental effects on the main rotor blades performance. Therefore, it is highly recommended that every helicopter pilot should be aware of the information gained in this work and accepts extensive training in simulating heavy rain situations.

Contents	
Abstract		II
Contents		IV
List of Figures	VI
List of Table	XI
Nomenclature	XII
Chapter 1 Introduction	1
Chapter 2 Research Background	5
2.1 Literature Review	5
2.2	Heavy Rain	14
Chapter 3 Numerical Modeling	19
3.1 Overview	19
3.2 Geometry Model Construction	20
3.3 Grid Generation	22
3.4 Governing Equations	25
3.5 Turbulence Modeling	25
3.6 Multiple Reference Frame (MRF) Capability	27
3.7 Flow Solver	29
3.8 Eulerian Model Capability	32
3.9 Discrete Phase Model (DPM) Capability	34
3.10 Verification	36
Chapter 4 Results and Discussion	42
4.1 Eulerian Model	43
4.2 Discrete Phase Model (DPM)	44
Chapter 5 Conclusions	67
References		70
 
List of Figures
Figure 2-1 Historical attempts of helicopter and airplane flight test. [1]	5
Figure 2-2 NACA 0012 airfoil.	6
Figure 2-3 The NASA model and experiments set-up. [5]	8
Figure 2-4 The NASA model profile. [5]	8
Figure 2-5 The UH-1H helicopter profile.	13
Figure 2-6 Characteristics of four surface water flow regions          :          1.Droplet-Impact Region; 2. Film-Convection Region;                 3. Rivulet-Formation Region; 4. Droplet-Convection Region. [15]	14
Figure 2-7 The droplet impact from film hole. [15]	15
Figure 2-8 Sketch of water behavior on top of wing surface. [16]	16
Figure 3-1 The NACA 0012 airfoil section profile.	20
Figure 3-2 The rotor blades profile.	20
Figure 3-3 The inside rotation profile.	21
Figure 3-4 The outside cube profile.	21
Figure 3-5 The far mesh of the rotor blades.	23
Figure 3-6 The rotation mesh of the rotor blades.	23
Figure 3-7 The near mesh of the rotor blades.	24
Figure 3-8 The near mesh of the blade face.	24
Figure 3-9 The solution loops of the pressure-based solver. [19]	31
Figure 3-10 The rotor blades use MRF situation.	37
Figure 3-11 The upper and lower surface result in inviscid and viscous of steady and unsteady condition compare with NASA experiment [5] in y/R=0.50.	38
Figure 3-12 The upper and lower surface result in inviscid and viscous of steady and unsteady condition compare with NASA experiment [5] in y/R=0.68.	39
Figure 3-13 The upper and lower surface result in inviscid and viscous of steady and unsteady condition compare with NASA experiment [5] in y/R=0.80.	39
Figure 3-14 The upper and lower surface result in inviscid and viscous of steady and unsteady condition compare with NASA experiment [5] in y/R=0.89.	40
Figure 3-15 The upper and lower surface result in inviscid and viscous of steady and unsteady condition compare with NASA experiment [5] in y/R=0.96.	40
Figure 4-1 The Discrete Phase Model global view of rain.	47
Figure 4-2 The Discrete Phase Model local view of rain droplets near rotor blades.	47
Figure 4-3 The two capabilities lift force comparison.	49
Figure 4-4 The upper and lower surface result at 650 rpm in y/R=0.50.	50
Figure 4-5 The upper and lower surface result at 650 rpm in y/R=0.68.	50
Figure 4-6 The upper and lower surface result at 650 rpm in y/R=0.80.	51
Figure 4-7 The upper and lower surface result at 650 rpm in y/R=0.89.	51
Figure 4-8 The upper and lower surface result at 650 rpm in y/R=0.96.	52
Figure 4-9 The upper and lower surface result at 1500 rpm in y/R=0.50.	52
Figure 4-10 The upper and lower surface result at 1500 rpm in y/R=0.68.	53
Figure 4-11 The upper and lower surface result at 1500 rpm in y/R=0.80.	53
Figure 4-12 The upper and lower surface result at 1500 rpm in y/R=0.89.	54
Figure 4-13 The upper and lower surface result at 1500 rpm in y/R=0.96.	54
Figure 4-14 The upper and lower surface result at 2400 rpm in y/R=0.50.	55
Figure 4-15 The upper and lower surface result at 2400 rpm in y/R=0.68.	55
Figure 4-16 The upper and lower surface result at 2400 rpm in y/R=0.80.	56
Figure 4-17 The upper and lower surface result at 2400 rpm in y/R=0.89.	56
Figure 4-18 The upper and lower surface result at 2400 rpm in y/R=0.96.	57
Figure 4-19 Top view of the blade velocity magnitude at 650 rpm with no rain and 4 mm droplet.	57
Figure 4-20 Top view of the blade velocity magnitude at 1500 rpm with no rain and 4 mm droplet.	58
Figure 4-21 Top view of the blade velocity magnitude at 2400 rpm with no rain and 4 mm droplet.	58
Figure 4-22 The blade velocity magnitude at 650 rpm in r/R = 0.96 (approaches the tip) with no rain and 4 mm droplet.	59
Figure 4-23 The blade velocity magnitude at 1500 rpm in r/R = 0.96 (approaches the tip) with no rain and 4 mm droplet.	59
Figure 4-24 The blade velocity magnitude at 2400 rpm in r/R = 0.96 (approaches the tip) with no rain and 4 mm droplet.	60
Figure 4-25 The blade vorticity magnitude at 650 rpm in r/R = 0.96 (approaches the tip) with no rain and 4 mm droplet.	60
Figure 4-26 The blade vorticity magnitude at 1500 rpm in r/R = 0.96 (approaches the tip) with no rain and 4 mm droplet.	61
Figure 4-27 The blade vorticity magnitude at 2400 rpm in r/R = 0.96 (approaches the tip) with no rain and 4 mm droplet.	61
Figure 4-28 The blade pressure contours at 650 rpm in r/R = 0.96 (approaches the tip) with no rain and 4 mm droplet.	62
Figure 4-29 The blade pressure contours at 1500 rpm in r/R = 0.96 (approaches the tip) with no rain and 4 mm droplet.	62
Figure 4-30 The blade pressure contours at 2400 rpm in r/R = 0.96 (approaches the tip) with no rain and 4 mm droplet.	63
Figure 4-31 The lift force comparison.	65
Figure 4-32 The lift force degradation rate comparison.	66

 
List of Table
Table 1 The Eulerian Model set parameters in FLUENT.	43
Table 2 The Eulerian Model lift force effect.	43
Table 3 The Discrete Phase Model (DPM) set parameters in FLUENT.	46
Table 4 The Discrete Phase Model (DPM) lift force effect.	46
Table 5 The Discrete Phase Model (DPM) lift force effect  at different rotatational speed.	65

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[19]	Fluent’s User Guide
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